added pseudo classes
added placeholder for five elements
added filter example
added pseudo element example
added impart stylesheet conditionally
added example for vertical center alignment
added optimize selectors
added text for sprites
added text preprocessor
clean question list and references
upgraded float and clear
added deleted scenes
removed need more
added read selector from css tricks
down grade speciity
major reordering of the contents
added inline and block
added question about descendent selectors
added top 6 links
added 6 more links